Flynn was accused of falsely telling the FBI that he had not talked about sanctions with the Russian ambassador to the U.S. during a December 2016 meeting, according to prosecutors with the office of Special Counsel Robert Mueller, the AP reported.

Flynn was interviewed by the FBI just days after Trump's inauguration. He then resigned in February 2017 after the White House said Flynn had misled them about whether he had discussed sanctions with the ambassador, Sergey Kislyak, the AP said.

In court today, Flynn admitted that a senior member of Trump's transition team directed him to contact Russian officials.

As he walked into a Washington D.C. area court, people shouted "Lock him up!" - a twist on the very slogan Flynn had aimed at presidential candidate Hillary Clinton while he campaigned for Trump.

As he walked in flanked by lawyers, the longtime military general also was asked if he felt like he had betrayed his country.

Flynn offered no response.

With his guilty plea, Flynn became the first person who worked in the Trump White House to admit guilt as part of a broad investigation being led by Mueller, who is investigating alleged coordination between Russia and the Trump campaign to influence the outcome of the 2016 election, the AP said.

Michael Flynn

Former Trump national security adviser Michael Flynn arrives at federal court in Washington, Friday, Dec. 1, 2017. Court documents show Flynn, an early and vocal supporter on the campaign trail of President Donald Trump whose business dealings and foreign interactions made him a central focus of Mueller's investigation, will admit to lying about his conversations with Russia's ambassador to the United States during the transition period before Trump's inauguration. (AP Photo/Susan Walsh)